1) Field of the Invention
The invention relates to solid electrolyte fuel cells and, more particularly, to reformer supported solid electrolyte fuel cells.
2) Description of the Prior Art
Fuel cells are electrochemical devices that convert chemical energy in fuels (such as hydrogen, methane, butane or even gasoline and diesel) into electrical energy by exploiting the natural tendency of oxygen and hydrogen to react. By controlling the means by which such reaction occurs and directing the reaction through a device, it is possible to harvest the energy given off by the reaction.
One of the important applications for solid oxide fuel cells (hereinafter referred to as SOFC) are auxiliary power units (APU) for transportation applications. A SOFC APU generates power using hydrogen and carbon monoxide reformed from fuels such as gasoline, diesel, natural gas, biodiesel, and the like.
SOFC are now considered for distributed power generation with natural gas being the major fuel. Researchers and Industry are looking for lowering the working temperature of these SOFC down to 500 to 700° C. At these medium operating temperature, major innovations can be integrated in the design of the SOFC. The reformer operating temperature should be considered as a major design criterion for the SOFC. Researchers have shown that 500° C. can be considered a lower temperature limit for a high conversion of the natural gas. Furthermore, the overall performance of the SOFC is directly inversely proportional to the electrodes thickness which drives ohmic losses and to the electrolyte thickness which drives the ionic conductivity and operating temperatures of the electrolyte. However, certain considerations of the flow of electrons along the very small thickness of the anode and the cathode will increase the electrical resistivity and special attention has to be given.
One can distinguish three designs for the SOFC: (a) the cathode supported SOFC (i.e. Westinghouse now Siemens in Pittsburgh), (b) the electrolyte supported SOFC (Siemens Erlangen Germany), and (c) the anode supported SOFC (Centre for Atomic Energy in Julich Germany).